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Equity Method Investments, Equity Method Investments (Details) (USD $)
In Millions, unless otherwise specified
Nov. 30, 2014
Aug. 31, 2014
Nov. 30, 2013
Schedule of Equity Method Investments [Line Items]      
Carrying value $ 7,335us-gaap_EquityMethodInvestments $ 7,248us-gaap_EquityMethodInvestments $ 6,439us-gaap_EquityMethodInvestments
Alliance Boots [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 7,335us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember		 7,248us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember		 6,439us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember
Ownership percentage (in hundredths) 45.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember		 45.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember		 45.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsMember
Other [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 71us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 74us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 7us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember
Other [Member] | Minimum [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership percentage (in hundredths) 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember
Other [Member] | Maximum [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership percentage (in hundredths) 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember		 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_OtherEquityMethodInvestmentsMember
Total [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value $ 7,406us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsAndOtherEquityMethodInvestmentsMember		 $ 7,322us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsAndOtherEquityMethodInvestmentsMember		 $ 6,446us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= wag_AllianceBootsAndOtherEquityMethodInvestmentsMember